Method for producing a starting material for the production of metallic components having regions of different strength

ABSTRACT

A method for producing a semifinished material for the production of metallic components having regions of different strength may involve, in a first step, providing thermal energy to a first region of the semifinished material that is uncoated such that the first region is heated and a material structure in the first region is converted at least partially into austenite. Meanwhile, thermal energy may prevented from being supplied to a second region of the semifinished material. In a second step following the first step, the first region may be cooled such that the material structure in the first region is converted at least partially into martensite.

PRIOR ART

The present invention relates to a method for producing a semifinished material for the production of metallic components having regions of different strength.

Components having regions of different strength are used in automotive construction, for example. In the case of such components, increased strengths are usually provided in those regions which are intended to be deformed only to a small degree in the event of a crash. Regions with low strength, by contrast, can deform to a greater extent in the event of a crash, and in the process absorb the high impact energies which arise in the event of a crash.

Components of this type can be produced, for example, by what is termed tailored tempering. Tailored tempering is a hot forming process in which generally coated semifinished materials, for example coated shaped blanks, are heated as a whole in a temperature range of 880° C. to 950° C., and then hot-formed in a forming tool. The forming tool comprises a plurality of temperature zones, by means of which the metal sheet is cooled at different speeds. This gives rise to a component having locally different strength properties. A martensitic material structure is formed in the rapidly cooled regions, and therefore these regions have an increased strength. Those regions which are cooled slowly have a reduced strength. Although this method has proved to be quite suitable in practice, it has been found to be disadvantageous that a relatively high expenditure of time is required for producing the soft regions.

DISCLOSURE OF THE INVENTION

The object of the present invention is that of reducing the time required for producing metallic components having regionally different strength properties.

The object is achieved by a method for producing a semifinished material for the production of metallic components having regions of different strength, wherein,

-   -   in a first step, a first region of the semifinished material,         which is provided in uncoated form, is supplied with thermal         energy, such that the first region is heated and the material         structure in the first region is converted at least partially         into austenite, while no thermal energy is supplied to a second         region of the semifinished material, and,     -   in a second step following the first step, the first region is         cooled, such that the material structure in the first region is         converted at least partially into martensite.

In the method according to the invention, the uncoated semifinished material is hardened in a first region, such as to give a first region having a strength which is increased compared to a second region. It is not necessary to heat the second region and to allow it to cool slowly in order to obtain regions having a strength which is reduced compared to the first region. It is thereby possible to reduce the time which is required to produce regions having different strength properties. Furthermore, a component having regions of different strength can be produced by means of cold forming, in particular by deep drawing or roll profiling.

The uncoated semifinished material preferably contains iron, and particularly preferably is a steel material. The uncoated semifinished material can be in the form of a hot strip obtained by hot rolling. Alternatively, the uncoated semifinished material may be a cold strip obtained by cold rolling. As a further alternative, the uncoated semifinished material can be configured as a shaped blank. Shaped blanks of this type can be obtained, for example, by being cut off from a hot strip or a cold strip. Furthermore, it is possible for the shaped blank to already have a two-dimensional basic form of the component to be produced.

The uncoated semifinished material preferably does not comprise any layer applied to the surface of the semifinished material. It is particularly preferable that the uncoated semifinished material is not zinc-plated or galvanized. The use of an uncoated semifinished material means that there is no need to be afraid of the occurrence of undesirable changes to the semifinished material and/or any coating of the semifinished material owing to the heating of the first region and/or the subsequent rapid cooling of the first region.

One advantageous embodiment provides that the thermal energy is supplied by way of a laser. The laser makes it possible to focus the energy emitted thereby onto a prespecified region, such that this region is heated. Alternatively, the thermal energy can be supplied by way of one or more induction coils. By way of the induction coil, it is possible to inductively heat the first region.

The first region of the semifinished material preferably has a strip-shaped form. Particularly in the case of a strip-shaped semifinished material, such as for example a hot strip or a cold strip, it is possible to produce a strip-shaped first region with increased strength by firstly guiding the strip-shaped semifinished material to an energy supply device, such as a laser or an induction coil, and thereafter cooling it. The cooling can be effected by guiding the strip-shaped semifinished material to a cooling apparatus after it has been guided to the energy supply device. The cooling apparatus can be used to apply a gaseous and/or liquid cooling medium to the first region of the semifinished material, in order to cool the semifinished material in the first region.

According to one advantageous embodiment, the first region—to which thermal energy is supplied—comprises a plurality of strip-shaped first portions which are separated from one another by a strip-shaped second portion of the second region—to which no thermal energy is supplied. It is thereby possible to obtain a semifinished material which comprises strip-shaped regions with high and low strength which alternate with one another. Semifinished material of this type may be used for the production of those components for automotive construction which absorb impact energy in the event of a crash and in the process are to be deformed in a controlled manner, such as for example a crash box or a longitudinal member. The strip-shaped regions of different strength which alternate with one another can be folded together like an accordion in the event of a crash.

In this context, it has proved to be preferable if a plurality of adjacent strip-shaped first portions have an identical center-to-center spacing, such that substantially uniform folding can occur in the event of a crash. The strip-shaped first portions may furthermore have an identical width.

Alternatively, a plurality of adjacent strip-shaped first portions may be formed in such a manner that they have different center-to-center spacings. By selecting different center-to-center spacings, it is possible to set a nonuniform folding behavior of the component in the event of a crash.

One preferred embodiment provides that, in the first step, a third region of the semifinished material is supplied with thermal energy in such a manner that the third region is heated to a higher temperature than the first region, and that the third region is likewise cooled in the second step. In this way, a higher proportion of the material structure can be converted into austenite in the third region than in the first region. During the subsequent cooling of the first region and of the third region, a higher strength is achieved in the third region than in the first region. In this respect, it is possible to produce different regions having an individually increased strength in the semifinished material.

According to a further advantageous embodiment, the semifinished material has a material thickness and the thermal energy is supplied in the first region in a manner distributed inhomogeneously over the material thickness. In this respect, the thermal energy is supplied in a manner which is not distributed uniformly over the entire material thickness, but instead only a selected subregion of the material cross section is exposed to an increased thermal energy, while another subregion of the material cross section is not exposed to thermal energy at all, or is exposed to thermal energy only to a small extent. It is thereby possible to produce a region in the semifinished material which has a strength profile distributed inhomogeneously over the material thickness. The energy is preferably supplied inhomogeneously by way of a laser, it being possible for a maximum of the energy output to be set by way of the optics of the laser. The material thickness of the semifinished material is preferably greater than 2 mm, particularly preferably greater than 3 mm.

In this context, it has proved to be particularly advantageous if a maximum of the supplied thermal energy is arranged in an inner region, in particular in the center, of the semifinished material, such as to produce a first region in which the surfaces of the semifinished material have a lower strength than the inner region. Regions treated in this way can be bent and/or chamfered in a subsequent processing step, with the risk of undesired breaking of the semifinished material being reduced.

According to one advantageous embodiment, the semifinished material is formed by cold rolling and/or by warm rolling after the thermal energy has been supplied to the first region. In this context, cold rolling is to be understood as rolling of the semifinished material at room temperature. Warm rolling is understood to mean rolling of the semifinished material at a warm rolling temperature which is increased compared to room temperature, the warm rolling temperature being selected in such a manner that the semifinished material does not undergo austenitization. The contact of the semifinished material with the rollers makes it possible for thermal energy to be transferred to the rollers, such that the cooling of the semifinished material can be promoted. As an alternative or in addition, the semifinished material can be wound up, in particular onto a coil, after the thermal energy has been supplied to the first region. As it is being wound up, individual layers of the semifinished material can come into contact with one another, and therefore the thermal energy which is absorbed in the heated first region can be discharged into other layers of the semifinished material. As a result, the cooling of the first region can be promoted.

According to an alternative, preferred embodiment, the semifinished material is formed by pressing, in particular in a plate press, after the thermal energy has been supplied to the first region. During the pressing, thermal energy can be discharged into a pressing tool, in particular a pressing plate, of the press, such that the cooling of the semifinished material is promoted. It is particularly preferable for the pressing tool, in particular the pressing plate, to be actively cooled.

It is furthermore advantageous if the semifinished material is coated in a third step following the second step. The coating, which follows the heating and cooling of the first region, makes it possible for the surface of the semifinished material to be protected against corrosion and/or against external influences, without it being necessary to fear a situation in which the coating is influenced by the heating and cooling. It is particularly advantageous if the semifinished material is coated by electrolytic means, for example is subjected to electrolytic zinc plating. Alternatively, the semifinished material may be subjected to hot-dip coating, in particular hot-dip galvanizing.

The object mentioned in the introduction is furthermore achieved by the contribution of an apparatus for producing a semifinished material for the production of metallic components having regions of different strength, comprising:

-   -   an energy supply device for supplying thermal energy to the         semifinished material, which is uncoated, in a first region,         such that the first region is heated and the material structure         in the first region is converted at least partially into         austenite, while no thermal energy is supplied to a second         region of the semifinished material, and     -   a cooling apparatus for cooling the first region, such that the         material structure in the first region is converted at least         partially into martensite.

For the apparatus, it is possible to achieve the same advantages as have already been described in conjunction with the method according to the invention.

The energy supply device preferably comprises a laser or an induction coil.

According to one advantageous embodiment, the apparatus comprises a conveying device for conveying the semifinished material in a direction of transport. Provision is preferably made of a plurality of energy supply devices, which are arranged spaced apart from one another along a transverse direction arranged transversely, in particular perpendicularly, to the direction of transport, such that the semifinished material can be guided past the energy supply devices. It is particularly preferable for provision to be made of a plurality of cooling apparatuses, which are likewise arranged spaced apart from one another along a transverse direction. The cooling apparatuses are preferably arranged in such a manner that the semifinished material conveyed along the direction of transport is guided firstly past the energy supply devices and thereafter past the cooling apparatuses.

Further details, features and advantages of the invention become apparent from the drawing and also from the following description of preferred embodiments with reference to the drawing. In this respect, the drawing merely illustrates an exemplary embodiment of the invention which does not have a limiting effect on the concept of the invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a perspective illustration of an exemplary embodiment of an apparatus for producing a semifinished material for the production of metallic components having regions of different strength.

EMBODIMENTS OF THE INVENTION

FIG. 1 shows, by way of example, an apparatus 1, by means of which semifinished materials 10 for metallic components having regions of different strength are produced for automotive construction.

As starting material, an uncoated semifinished material 10, preferably composed of a steel material, particularly preferably composed of a manganese-boron steel, of strip-shaped form is supplied to the apparatus 1. The semifinished material 10 may be a hot strip or cold strip. The semifinished material 10 is provided in a manner wound up onto a coil 2. During the processing, the semifinished material 10 is unwound from the coil 2 and conveyed in a direction of transport T by way of a conveying device (not shown).

The semifinished material 10 is guided by means of the conveying device firstly past a plurality of energy supply devices 3, by way of which a first region 5 of the semifinished material 10 is supplied with thermal energy. As a consequence of the thermal energy being supplied to it, the first region 5 is heated above the Ac1 temperature of the semifinished material 10, preferably above the Ac3 temperature of the semifinished material 10, and the material structure in the first region 5 is converted at least partially, preferably completely, into austenite. The energy supply devices 3 introduce the thermal energy exclusively into the first region 5 of the semifinished material 10. A second region 6 of the semifinished material 10, which does not pass into the region of influence of the energy supply devices 3 when the semifinished material 10 is guided past the energy supply devices 3, is not exposed to thermal energy. This means that—contrary to the first region—no conversion of the material structure into austenite occurs in the second region.

The energy supply devices 3 are arranged spaced apart from one another on a straight line, which runs along a transverse direction Q arranged perpendicular to the direction of transport T. The energy supply devices 3 each comprise a laser or an induction coil. The spaced-apart arrangement of the energy supply devices 3 produces a first region 5 comprising strip-shaped first portions 5.1, 5.2, which are separated from one another in each case by a strip-shaped second portion 6.1 of the second region 6. In the exemplary embodiment, adjacent strip-shaped first portions 5.1, 5.2 have different center-to-center spacings. In one modification of the exemplary embodiment, in which the energy supply apparatuses 3 are separated by identical spacings, it is possible for strip-shaped portions of the first region 5 which have identical center-to-center spacings to be produced.

Once the semifinished material 10 has been guided past the energy supply devices 3, the semifinished material 10 is guided past a plurality of cooling apparatuses 4. By means of the cooling apparatuses 4, the heated first region 5 of the semifinished material 10 is cooled in such a manner that the material structure in the first region is converted at least partially into martensite. This gives rise to a first region 5 which has an increased strength compared to the second region 6.

The cooling apparatuses 4 are arranged spaced apart from one another on a straight line, which runs along a transverse direction Q arranged perpendicular to the direction of transport T. The spacings of the cooling apparatuses 4 are selected in such a manner that a portion 5.1, 5.2 of the first region 5 is supplied to a cooling apparatus 4 after it has been heated by an energy supply apparatus 3. A gaseous and/or liquid cooling medium is applied to the semifinished material 10, in particular the first region 5 of the semifinished material 10, by way of the cooling apparatuses 4.

In this respect, the uncoated semifinished material 10 is hardened in the first region 5, with the second region 6 not being hardened and essentially retaining its original strength. Heating of the second region 6 is not required.

Following the regional hardening described above, the semifinished material 10 is cold-rolled and/or warm-rolled. In addition, the semifinished material 10 is coated (zinc-plated), for example by an electrolytic coating method or hot-dip coating.

According to one modification of the exemplary embodiment shown in FIG. 1, the thermal energy is introduced differently by way of a plurality of energy supply apparatuses 3 in such a manner that a higher temperature is reached in a third region than in the first region 5. A temperature between the Ac1 temperature and the Ac3 temperature can be set in the first region and a temperature above the Ac3 temperature of the semifinished material 1 can be set in the third region. A higher proportion of the structure is therefore austenitized in the third region than in the first region 5. Both the first region 5 and the third region are cooled by way of the cooling apparatuses 4, and therefore a martensitic material structure is formed in the first region 5 and in the third region, the third region having an increased strength compared to the first region.

As an alternative or in addition, the thermal energy can be supplied in the first region and/or in the third region in a manner distributed inhomogeneously over the material thickness of the semifinished material 10. As a result, a strength profile distributed inhomogeneously over the material thickness can be produced. In this respect, the energy is preferably supplied by way of a laser, it being possible for a maximum of the energy output to be set by way of the optics of the laser. By way of example, the laser can be focused in such a manner that a maximum of the supplied thermal energy is arranged in an inner region of the semifinished material. This produces a first region and/or third region in which the surfaces of the semifinished material have a lower strength than the inner region.

According to a further modification of the exemplary embodiment described above, use is made of a semifinished material 10 which is configured as an uncoated shaped blank.

LIST OF REFERENCE SIGNS

-   1 Production apparatus -   2 Coil -   3 Energy supply device -   4 Cooling apparatuses -   5 First region -   5.1 First portion of the first region -   5.2 Second portion of the first region -   6 Second region -   6.1 Portion of the second region -   10 Semifinished material -   Q Transverse direction -   T Direction of transport 

1-13. (canceled)
 14. A method for producing a semifinished material for production of a metallic component having regions of different strength, the method comprising: supplying thermal energy to a first region of the semifinished material that is uncoated such that the first region is heated and a material structure in the first region is converted at least partially into austenite, wherein the thermal energy is prevented from being supplied to a second region of the semifinished material; and cooling the first region following the supply of the thermal energy such that the material structure in the first region is converted at least partially into martensite.
 15. The method of claim 14 wherein the thermal energy is supplied by way of a laser or an induction coil.
 16. The method of claim 14 wherein the first region has a strip-shaped form.
 17. The method of claim 14 wherein the first region comprises a plurality of strip-shaped portions that are separated from one another by strip-shaped portions of the second region.
 18. The method of claim 17 wherein the plurality of strip-shaped portions in the first region have the same center-to-center spacings.
 19. The method of claim 17 wherein the plurality of strip-shaped portions in the first region have different center-to-center spacings. cm
 20. The method of claim 14 wherein supplying the thermal energy comprises supplying a third region of the semifinished material with the thermal energy such that the third region is heated to a higher temperature than the first region, wherein the cooling comprises cooling the third region.
 21. The method of claim 14 wherein the semifinished material has a material thickness, wherein the thermal energy is supplied to the first region in a manner such that the thermal energy is distributed inhomogeneously over the material thickness.
 22. The method of claim 21 wherein a maximum of the supplied thermal energy is arranged in an inner region of the semifinished material.
 23. The method of claim 14 comprising forming the semifinished material by at least one of cold rolling or warm rolling after the thermal energy is supplied to the first region.
 24. The method of claim 14 comprising forming the semifinished material by pressing after the thermal energy is supplied to the first region.
 25. The method of claim 14 comprising forming the semifinished material by pressing the semifinished material in a plate press after the thermal energy is supplied to the first region.
 26. The method of claim 14 comprising coating the semifinished material after the first region of the semifinished material is cooled.
 27. An apparatus for producing a semifinished material for production of a metallic component having regions of different strength, the apparatus comprising: an energy supply device for supplying thermal energy to a first region of the semifinished material that is uncoated such that the first region is heated and a material structure in the first region is converted at least partially into austenite, wherein the energy supply device prevents the thermal energy from being supplied to a second region of the semifinished material; and a cooling apparatus for cooling the first region such that the material structure in the first region is converted at least partially into martensite. 